Little is known about the cellular mechanisms of pancreatic electrolyte secretion because of the complex geometry of the pancreas. A new preparation is now available to study secretion kinetically at the cellular level. Uptake of Na22 into stripes of rabbit pancreas in vitro follow two compartment kinetics (Rothman, S.S., in The Exocrine Pancreas, Ed. I.T. Beck and D.G. Sinclair, Churchill, London (1917). Superficially one compartment behaves as the cellular phase of pancreatic tissue and the other as the volume of ductal juice in the tissue. In this investigation, compartmental analysis of isotope uptake into the in vitro pancreas strip preparation will be used to study the cellular mechanisms of electrolyte secretion. Initial work will be devoted to a careful characterization of the tissue for compartmental analysis including development of a kinetic model for uptake, quantitative identification of the compartments, and independently measuring kinetics parameters in the model. Once a satisfactory compartmental model has been developed, it will be used to study secretory mechanisms with primary emphasis on the active transport of Na and HCO3 and possible coupling between their transport mechanisms. Finally information should also be gained on epithelial transport in general since it should be possible to study transport simultaneously across both the functionally distinct cell membranes in an epithelial tissue.